Phylogeny and Systematic Position of Zosterodasys (Ciliophora, Synhymeniida): A Combined Analysis of Ciliate Relationships Using Morphological and Molecular Data

Abstract

The Synhymeniida is characterized both by a band of somatic dikinetids, the synhymenium, extending across the surface of the cell and by a ventral cell mouth lacking specialized feeding cilia but subtended by a well-developed cyrtos. The synhymeniids have been hypothesized to be members of the class Nassophorea but our previous ultrastructural study of the synhymeniid genus Zosterodasys did not show any clear synapomorphies that would permit definitive placement in the Nassophorea or as a sister taxon to any of the other ciliate groups possessing a cyrtos. In the present study, simultaneous analysis of morphological and small subunit rDNA molecular data indicates that the Synhymeniida are sister to the class Phyllopharyngea and that this clade is, in turn, sister to the remaining Nassophorea, although this result is sensitive to dataset inclusion and alignment parameters. While this suggests that taxa with a ventral cyrtos might be united into a named taxon (e.g. resurrecting the Hypostomata), additional data are needed to reach a definitive conclusion.

Phylogenetic study of Class Armophorea (Alveolata, Ciliophora) based on 18S-rDNA data

“…This situation is aggravated by differences in the placement of ‘difficult’ positions for each combination of parameters. These findings not only corroborate previous observations based on cladistic analyses of implied-aligned matrices of ciliate 18S rRNA (Kivimaki et al , 2009), but also emphasize the need for thorough indel parameter exploration during automated nucleotide alignments (Morrison and Ellis, 1997; Carroll et al , 2006; Smythe et al , 2006; Kjer et al , 2007). …”

“…The sensitivity of data to nucleotide alignment parameters and character weighting (Wheeler, 1995; Morrison and Ellis, 1997; Hall, 2005; Kjer et al , 2007; Goloboff et al , 2008; Dessimoz and Gil, 2010) is related to differences in phylogenetic hypotheses. This has already been demonstrated for ciliates by Kivimaki et al (2009), although their study did not include data on armophoreans. Inconsistencies among phylogenies may reflect the properties of the analytical frameworks used, i.e.…”

The Revised Classification of Eukaryotes

“…Based on SSU rRNA gene sequences, the Nassophorea with the synhymeniids transferred to the Phyllopharyngea may still not be monophyletic Kivimaki et al 2009).…”

Comparative Genomics Analysis of Ciliates Provides Insights on the Evolutionary History Within “Nassophorea–Synhymenia–Phyllopharyngea” Assemblage

“…Members of the order Synhymeniida are characterized by a cytopharyngeal basket of well-developed nematodesmata bound proximally by the presence of a band of somatic dikinetid cilia (Kivimaki et al, 2009 ; Figure 1). Corliss assigned the Synhymeniida to the subclass Hypostomata and placed the nassulids and microthoracids in a separate order (Nassulida) within the same subclass (Corliss, 1979; Table 1).…”